Batteries are commonly used as energy sources. Typically, a battery includes a negative electrode (anode) and a positive electrode (cathode). The anode and cathode are often disposed in an electrolytic solution. During discharge of a battery, a chemical reaction can occur that oxidizes an active anode material and reduces an active cathode material. During the reaction, electrons flow from the anode to the cathode, and ions in the electrolytic solution flow between the anode and the cathode. Certain batteries can be recharged by running the chemical reaction in reverse.
One type of battery is a lead acid battery. In a lead acid battery, lead is usually an active anode material, and lead dioxide is usually an active cathode material. Generally, lead acid batteries also contain sulfuric acid, which serves as an electrolyte and participates in the chemical reaction. A typical discharge reaction for a lead acid battery reaction is:
                    Anode        :                                                  Pb            (            s            )                    +                                    HSO              4              -                        ⁡                          (              aq              )                                      →                                            PbSO              4                        ⁡                          (              s              )                                +                      H            +                    +                      2            ⁢                          e              -                                                              Cathode        :                                                                                PbO                2                            ⁡                              (                s                )                                      +                          3              ⁢                                                H                  +                                ⁡                                  (                  aq                  )                                                      +                                          HSO                4                -                            ⁡                              (                aq                )                                      +                          2              ⁢                              e                -                                              →                                                    PbSO                4                            ⁡                              (                s                )                                      +                          2              ⁢                              H                2                            ⁢              O                                      _                                Net        :                                                  Pb            (            s            )                    +                                    PbO              2                        ⁡                          (              s              )                                +                      2            ⁢                                          H                +                            ⁡                              (                aq                )                                              +                      2            ⁢                                          HSO                4                -                            ⁡                              (                aq                )                                                    →                              2            ⁢                                          PbSO                4                            ⁡                              (                s                )                                              +                      2            ⁢                          H              2                        ⁢            O                              